By way of example, in a photolithography process of a semiconductor device manufacturing process, a series of processes including a resist coating process of coating a resist liquid onto a wafer to form a resist film, an exposure process of exposing the resist film to a preset pattern, and a developing process of developing the exposed resist film is performed in sequence, so that a preset resist pattern is formed on the wafer. The series of processes is performed in a coating and developing system as a substrate processing system including various processing units configured to process the wafer and a transfer device configured to transfer the wafer.
One of defects occurring on the wafer processed in the coating and developing system is a defocus defect caused by a defocus during the exposure process. The main cause of the defocus defect is that a stage of an exposure apparatus is contaminated with particles. The contamination of the stage is caused by particles adhering to, in particular, a rear surface of the wafer loaded into the exposure apparatus. For this reason, the wafer before being loaded into the exposure apparatus needs to have a clean rear surface.
Further, the inside of the exposure apparatus is in a high vacuum, and for example, during an operation of cleaning the contaminated stage of the exposure apparatus, the exposure apparatus is open to atmosphere, and after the cleaning operation, the exposure apparatus needs to be exhausted again to a high vacuum level. For this reason, this cleaning operation requires a lot of time and the coating and developing system cannot be operated during the cleaning operation, which is a problem in terms of productivity.
In this regard, Patent Document 1 suggests a substrate processing system including a cleaning unit configured to clean the rear surface of the wafer to keep the rear surface of the wafer loaded into the exposure apparatus clean and an inspection unit configured to image the cleaned rear surface of the wafer with an imaging device such as a CCD line sensor.
In this substrate processing system, wafers cleaned by the cleaning unit are inspected by the inspection unit, and only wafers, which are confirmed as having particles in a tolerance range, are loaded into the exposure apparatus. Thus, it is possible to reduce defocus defect and contamination of the stage.
Patent Document 1: Japanese Patent Laid-open Publication No. 2008-135583
However, even if only the wafers, which are confirmed as having particles in the tolerance range after being cleaned by the cleaning unit and inspected by the inspection unit, are loaded into the exposure apparatus, a defocus defect may still occur.
In this regard, the present inventors assumed that a cause of the defocus defect is that multiple wafers having particles in the tolerance range are repeatedly transferred so that the particles are gradually deposited at the same position on the stage and grow to an intolerable size.
In order to avoid the defocus defect caused by the deposition of particles in the tolerance range, for example, it is considered to more strictly set the tolerance range of particles. However, in this case, even wafers, which have conventionally undergone the exposure process without any problems, cannot pass this inspection, and, thus, it is not practical. Therefore, the present inventors assumed that it is possible to reduce the defocus defects caused by the particle growth if a tendency of defects which include particles and occur in a surface of the wafer is cumulatively checked and particles are suppressed from being continuously deposited, for example, at the same position on the stage.